1. Field of the Invention
The present invention relates to a ringed tubular sheath which is slit along a longitudinal cut in the sheath.
2. Description of the Related Art
Ringed tubular sheaths, that is to say ones whose shape resembles a succession of rings connected to one another, are usually made of extruded plastic materials such as polypropylene, polyamide or polyesters. These sheaths make it possible to produce complex protective networks for bundles of electrical wires or cables within ships, aircraft or automobile vehicles and, particularly in this latter case, in the engine compartment. This type of process is described in greater detail, for example, in documents FR 2 171 844, GB 1 250 639 and GB 1 311 205.
In order to permit the installation of the wires or cables inside these sheaths, the latter are slit. That is to say, they have been cut along a longitudinal straight line at the end of the manufacturing process. It is then possible to introduce electrical wires and cables later, in any zone of the sheath, directly through the slit. One of the main characteristics of a slit ringed tube is its capacity for closing up again after being opened, this characteristic being provided by the resilience of the vertical walls of the ringed portions.
These protective sheaths may have more or less elaborate systems of closures in order to prevent the tube from allowing the wires to escape in zones having low radii of curvature, where the slit tends to open up again. A number of known documents describe these types of sheath, in particular DE-U-89 030 70, EP 0 114 213, DE 34 05552 and WO 97 323 79.
Although they are satisfactory in the majority of cases, a number of drawbacks are nevertheless found to remain. On the one hand, the force required to open the sheath, with or without a closing system, is too great. The sheaths may thus be strongly resistant at the time of introduction of the cables and often, when the latter are being installed, the operator is obliged to use a tool in order to enable him to introduce the cables and wires without injuring himself.
On the other hand, the installation of the components produces an irreversible deformation of the ringed portions, so the return to the initial position is more awkward. Under these circumstances, the tube may have a slit of several tenths of a millimetre (or even several millimetres), and this constitutes a drawback as regards the protection of the wires or cables that are present inside. The permanent deformation of the tube in the course of opening is linked to the fact that the plastic material has passed beyond its zone of elastic deformation.
Finally, in the case of sheaths with a closing system, the latter gives rise, because of its non-ringed shape, to a rigidity which is ill-suited to the routing of the cables.
Japanese Patent Application JP 2000 115945 discloses a ringed and slit tubular sheath comprising one or more longitudinal grooves disposed at 45° on either side of the longitudinal cut. The grooves extend from the peak to the trough of the corrugations, but without passing through the wall forming the common base of the trough of the corrugations, so as to function as hinges that facilitate the introduction of the cables into the interior of the slit sheath.
European Patent Application EP 859 440 discloses a ringed and slit tubular sheath comprising corrugations of reduced height in the region in which the longitudinal cut is made, so as to create a hinge effect between each edge of the slit and the rest of the periphery of the sheath. This results in greater ease of introduction of the cables into the interior of the slit sheath.
In these two known examples, the hinge effect is the result of a reduction in the thickness of the sheath. This reduction in thickness can lead to wearing and tearing of the sheath in the region of the hinge.
The object of the invention is to overcome the drawbacks indicated above.